Preformed and newly formed mediators released from mast cells play a central role in protective or pathologic immediate hypersensitivity reactions. Mast cell mediator release also appears to contribute to some complement-mediated reactions, to the expression or regulation of lymphocyte-mediated reactions, to some forms of nonspecific inflammation, and to some physiologic responses. The long term objectives of this proposal are to resolve the biochemical basis of mast cell membrane fusion - the mechanism of preformed mediators release; and the release of arachidonic acid - the precursor of several newly formed mediators. Recent experiments in this and other laboratories have provided biologic precedents and direct evidence in rat mast cells that alterations in the metabolism of sn-1,2-diacylglycerol (DAG) and of phosphatidic acid (PA) may play pivotal roles in mast cell mediator release. The specific aims of this proposal are: 1.) to examine the origins and fates of DAG in stimulated rat mast cells with particular emphasis on phospholipase C, phosphatidate phosphohydrolase, DAG kinase and DAG-lipase; 2.) to measure the levels, origins and fates of other fusogenic lipids in stimulated rat mast cells with emphasis on DAG, sn-1 or 2-monoacylglycerol and lysophospholipids; 3.) to examine the origins and fate of newly formed P A in stimulated mast cells; 4.) to determine the reactions that make arachidonic acid (AA) available for the synthesis of newly formed mediators in stimulated mast cells; 5.) to probe the intracellular systems that regulate these reactions; and 6.) to determine whether or not rat mast cells express protein kinase activity that is activated by DAG ("protein kinase C") and if present to characterize the activity in detail. Identification and characterization of the reactions that lead to membrane fusion and AA availability in mast cells are fundamental to an understanding of Ige-mediated reactions at the molecular level. Improved knowledge of the mechanisms of mediator release might permit the development of new approaches to purposeful regulation that in turn eventually might be applied to improve the management of human allergic or other inflammatory disorders.